An engine may stop one time in a position where engine cranking time is short and engine starting is fast after a first engine stop, and the same engine may stop a second time in a position where engine cranking is long and engine starting is slower. The engine may start fast if the engine is stopped at a position near intake valve closing time of one cylinder so that the engine reaches a top-dead-center compression position with a cylinder full air charge in a short duration of crankshaft rotation. On the other hand, the engine may take longer to start if the engine is stopped away from an intake valve closing time of an engine cylinder such that the engine crankshaft has to be rotated for a time before an intake valve closing of a cylinder occurs. Further, if combustion begins in a cylinder that has less than a full charge of air and fuel, the engine may not run-up in a desired manner and engine emissions may increase. Consequently, it may be desirable to provide short engine cranking and starting times so that vehicle occupants may not be exposed to inconsistent engine starting times. One way to improve engine starting is to preposition the engine before starting, but the engine may not stay at a desired engine stopping location.
The inventors herein have recognized the above-mentioned issues and have developed an engine operating method, comprising: a plurality of times, rotating and stopping rotation of an engine after an engine stop request and before an engine start request via a controller.
By rotating and stopping an engine a plurality of times after an engine stop request and before an engine start request, it may be possible to provide the technical result of prepositioning an engine for an engine start without the engine changing position after it reaches a desired engine stopping position that reduces engine starting time. Specifically, an engine may be rotated in small crankshaft angle increments and stopped before the engine is rotated again so that pressure in the engine cylinders is close to atmospheric pressure when the engine is finally stopped. This allows the engine to reach its desired final stop position before an engine start without rotating out of its desired final stop position due to pressures in engine cylinders. Consequently, the engine may be started from its desired stop position instead of starting from a position that increases engine cranking time or reduces combustion torque of a first combustion event since the most recent engine stop.
The present description may provide several advantages. In particular, the approach may provide more consistent engine starting times. Further, the approach may prevent the engine from having to be repositioned once it reaches its desired stopping position. Further still, the approach may reduce engine emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.